1. Field of the Invention
The invention relates to a dental material useful as a dental filling material, a dental adhesive primer or a pit and fissure sealant, where adhesion to the teeth is strongly required. In this specification, the term "dental material" is used to include dental filling materials, dental adhesive primers, and pit and fissure sealants.
2. Description of the Prior Art
The polymerizable monomers that have so far been used in dental materials are mainly methacrylate monomers. Typical examples are, as are disclosed, for example, in U.S. Pat. Nos. 3,066,112, 3,751,399 and 3,926,906, 2,2'-bis[4-(3-methacryloxy-2-hydroxypropoxy)phenyl]propane (hereinafter abbreviated to Bis-GMA), ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate and tetraethylene glycol dimethacrylate, which are actually in wide use. Particularly, Bis-GMA can be used for general purposes. Since it is highly viscous, however, it is diluted with a monomer having low viscosity, such as triethylene glycol dimethacrylate.
These dental materials are required to adhere to the teeth. When the above-mentioned polymerizable monomers are polymerized and hardened on the surface of the teeth, the cured product should adhere to the tooth surface. For that reason, in the prior art dental treatment, the tooth surface is etched with an acid such as phosphoric acid. This treatment removes a smeared layer on the tooth surface and causes formation of an uneven or coarse portion or portions on the tooth surface. Now the polymerizable monomer mixture, when applied, can enter those minute depressions formed by said acid etching, whereby adhesion of the cured material to the tooth surface may be secured. With the prior art dental materials, however, adhesion is still insufficient, as can be seen from the fact that repeated application of occlusal pressure or repeated thermal expansion and contraction is apt to cause formation of gaps between the teeth and the cured product, which may lead to falling off of the filled material, unfavorable change of the teeth at the site between the teeth and the cured product (e.g. secondary caries etc). Therefore, dental materials with improved adhesion have been expected. For improved adhesion, it is essential that the polymerizable monomer mixture can enter the depressions formed by acid etching to a sufficient extent, and that the polymerizable monomer mixture is desired to be low viscosity and wettable to the teeth, to satisfy the above object.
Improved adhesion to the teeth may be achieved not only by utilizing anchor effect brought about by the above-mentioned uneven portion or portions formed on the tooth surface but also by utilizing chemical bonding with enamel and dentin. For example, certain polymerizable monomers containing phosphoric acid diester groups as disclosed in German Offenlegungsschrift No. 2,711,234.1 have good chemical affinity for the dentin, and consequently the cured products from compositions containing such monomers have been found to be excellent in adhesion to the teeth. These monomers, however, are added in small amounts in view of their characteristics, and it is necessary to use in combination with other monomer or monomers. Combined use of monomers capable of wetting the teeth easily is more effective.